Self tooling, molded electronics packaging

ABSTRACT

A method of protecting an electronic component from the environment comprising the steps of providing a bag made from thermoplastic heat shrink material, inserting said electronic component into said bag, injecting a liquid polymerizable resin into said bag, heating said bag to shrink it about said electronic component and said resin, and curing said resin.

BACKGROUND OF THE INVENTION

Known methods of packaging electronic components generally entailenclosing the component in a specially designed container orencapsulating the components in a rigid media through dipping ormolding. Such high integrity packaging of electronic components,sometimes termed "potting," often amounts to a disproportionate share ofthe weight and cost of the electronic component assembly. Such knownmethods have inherent disadvantages, particularly when electricalshielding is required. Moreover, installation of the "potted" componentsgenerally requires a relatively large volume allocation.

This situation is ameliorated to some extent by the use of moldedpackaging. However, molding requires time intensive steps for dipping orother application operations. In the case of electronic components thatrequire grounded shielding for the suppression of electromagneticinterference, a second coating must be applied to the outer surface ofthe molded assembly. Since the vital outer coating must be protectedagainst damage, additional processing is generally required to insurethe integrity of the shielding.

SUMMARY OF THE INVENTION

The aforesaid problem is solved by a self tooling, multilayeredthermoplastic "shrink wrap" enclosure that is filled with a prescribedamount of an injectable low viscosity thermoset resin. Precalculatedshrink of the thermoplastic wrap over a measured amount of thermosetresin results, when the assembly is heated for shrink and cure, inminimum material usage and in a light weight, self tooled, rigidassembly. The resulting cured shape of the molded self tooled assemblywill be largely determined by the shape of the electronic components ormounting therefor. As the wrapping is exposed to heat and shrinks, itwill bridge the high points of the assembly's components. The finalcured shape need not be governed or altered by subsequent tooling orprocessing. Conductive shielding around the electronic components isprovided between layers of the shrink wrap. When heat shrink and cure ofthe assembly is completed, the conductive shielding is reliably sealedinternally of the outer plastic coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a circuit board having a plurality ofelectronic components mounted thereon;

FIG. 2 is a perspective view of the circuit board of FIG. 1 enclosedwithin a plurality of thermoplastic layers with a resin injection nozzleextending thereinto;

FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 2after heat shrink of the enclosure and cure of the thermoplastic resintherein;

FIG. 4 is a cross-sectional view taken substantially along the line 4--4of FIG. 3; and

FIG. 5 is a view similar to FIG. 3 of the completed shrink wrap package.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

As seen in FIG. 1 of the drawing, a circuit board 10 is provided with aplurality of electronic components 12, 14, 16, 18 and 20 which aresecured to the board 10 in the conventional manner.

In accordance With a preferred constructed embodiment of the instantinvention, the circuit board 10 is enclosed in a pair of plastic bags 22and 24. It is to be understood that the number of bags employed isdependent upon the characteristics of the electronic components andwhether the components are required to be electrically shielded fromelectromagnetic interference. As seen in FIG. 4, the outer bag 22encloses the internal bag 24, which is provided with an electricallyconductive metallic layer 26 suitable for shielding the components 12,14, 16, 18 and 20 of the circuit board 10.

The bags 22 and 24 may be formed as tubes and thereafter heat sealedalong edges 30 and 32 thereof to form an enclosure 34. The enclosure 34is provided with an air bleed sprue 36 to provide for the exhaust of airtrapped internally of the enclosure 34 upon the injection of resin 38thereinto as well as to provide for exit of air from the inside of theenclosure 34 upon shrink of the plastic bags 22 and 24. Resin isinjected through a resin injector tube 42.

As best seen in FIG. 5 of the drawing, the portion of the plastic bags22 and 24 surrounding a pair of terminals 50 and 52 extending from thecomponents 16 and 20 are ground away exposing the terminals 50 and 52for electrical connection to an electrical circuit. The shielding layer24 is provided with a ground terminal as may be required.

While the preferred embodiment of the invention has been disclosed, itshould be appreciated that the invention is susceptible of modificationwithout departing from the scope of the following claims.

I claim:
 1. A method of protecting an electronic component from theenvironment comprising the steps ofproviding a bag made fromthermoplastic heat shrink material, inserting said electronic componentinto said bag, injecting a liquid polymerizable resin into said bag,heating said bag to shrink it about said electronic component and saidresin and thereby exhaust air from within said bag, and curing saidresin.
 2. The method of claim 1 including the step of providing a secondbag and coating the surface of one of said bags that is juxtaposed tothe surface of the other of said bags with an electrically conductivecoating.
 3. The method of claim 1 wherein said bag and resin are heatedconcomitantly to effect shrinking and polymerization thereof,respectively.
 4. The method of claim 1 including the step of coating theexterior of said bag with an electrically conductive material andplacing said bag in an outer bag of thermoplastic heat shrinkablematerial.